Rotary hearth furnace control



Dec. 3, 1963 w. F. STEVENS ETAL 3,112,913

ROTARY HEARTH FURNACE CONTROL Filed March 28, 1961 2 Sheets-Sheet 1Fig.l.

Inventors Wiliium F. Stevens 8 George R. Bauer ited States Patent 3112,?318 Patented Dec. 3, i953,

ice

3,112,918 ROTARY HEARTH FURNACE CONTRGL Wiiliarn F. Stevens, Greentree,and George R. Bauer,

Bridgevilie, Pa, assignors to Salem-Brosius, Inc, Pittsburgh, Pin, acorporation of Pennsylvania Filed Mar. 28, 1961, Ser. No. 98,809 7Claims. (Cl. 263-7) This invention relates to rotary hearth furnaces andmore particularly to a control system for a rotary hearth furnace havingautomatic charging and discharging means.

Hearth positioning for charging and discharging has been formerlyaccomplished by use of hearth station switches such as shown anddescribed in United States Patent Number 2,622,861 to Talley. Basically,the hearth station switch is a geared type cam limit switch. In thehearth station switch, the cams are notched and the gearing provides aratio of cam revolutions to hearth revolutions. The number of stations,wherein the hearth is temporarily stopped for charging or dischargingthe articles being heated therein, is determined by choice of cams andgearing. The number of stations therefore is limited by the number ofnotches on a particular cam disc and the gear ratio used. Of course, aplurality or bank of cam discs may be provided to allow some flexibilityof choice; however, the fact remains that the number of stations islimited to the particular selection of cam discs available in the bank.For example, a bank may be comprised of as many as ten different cams.Each divides the hearth into a particular and different number ofstations or stops. use a hearth most efiiciently, the articles beingheated should be spaced as closely as possible, which means thatgenerally the most desirable spacing is some number and fraction ofinches. With a selection of only ten different divisions of stops, moreoften than not, the most eificient division is not available. Thus, asapractical matter, the operator has to settle for the cam and geararrangement that most nearly approaches the desired spacing. Sometimesthe desired number of station stops is not even nearly available in thedisc bank and the operator must change the cams or gears, i.e., re placethe cams or gears or both with ones that will come closer to providingthe number of hearth station stops desired. Such changes are ineflicientand time-consuming.

Such problems of efiicient spacing of billets on the hearth and offlexibility in choice of the number of sta- :tion stops are old and wellknown to those skilled in this art.

We have invented a control system in a rotary hearth furnace thatminimizes the above problems to the point of negligibility. We provide acounting system for control of a rotary hearth furnace comprising, incombination, a rotary hearth furnace having a rotatable hearth, hearthcharging means, hearth discharging means, hearth travel measuring meanshaving electric pulse generating and pulse counting means and controlmeans operatively responsive to said counting means coordinating thestarting and stopping of the hearth and the energizing and deenergizingof the charging means and discharging means including cycling meanscontrolling the duration of hearth stoppage. In our preferred embodimentthe hearth travel measuring means comprises disc means coaxially mountedon and rotating with the drive or jackshaft of the hearth drive means,said disc means having alternately light transmitting and opaqueportions, a light source and photosensitive element operativelyassociated with said disc means whereby portions of said disc meanspermit the passage of light from said source to said element as saiddisc rotates and electronic counting means operable to count said lightpassages.

Other details, objects and advantages of the invention will becomeapparent as the following description of a present preferred embodimentthereof proceeds.

In the accompanying drawings, we have shown a present preferredembodiment of the invention in which FIGURE 1 is a plan viewdiagrammatically illustrating a rotary hearth furnace with automaticcharging and discharging machines;

FIGURE 2 is a fragmentary isometric view of the hearth drive jackshaftand photoelectric counting mechanism associated therewith; and

FIGURE 3 is -a diagrammatic showing of a control system for a rotaryhearth furnace embodying our invention.

Refering now to FIGURE 1, we have illustrated generally a rotary hearthfurnace 10 having a rotatable hearth 11 in a furnace chamber 12. Acharging is.- chine 13- is disposed opposite a furnace chamber opening13a or charge door and automatically charges articles to be heated, suchas billets l4 and 15, into furnace chamber 12 and deposits them onhearth 11. A discharging machine 16- is disposed opposite anotherfurnace chamber opening 16a or discharge door and automaticallydischarges or removes the heated articles from the hearth and furnacechamber. The operation of the automatic charging and dischargingmachines is old and well known to those skilled in the art and will notbe further described in this specification. The automatic opening andclosing of the furnace chamber doors to facilitate charging anddischarging of articles on the hearth is likewise old and well known.

Rotating hearth i1 is driven by an electric motor 17 through adifferential gear unit 18 which revolves or rotates the jackshafts 19and 2h. The power from jackshafts 19 and 25 is transmitted respectivelythrough chain drives 21 and 22 to reducers 23 and 24 thence to piniongear-s 25 and 26 which engage ring gear 27 attached to hearth 11 andthus rotates the hearth. It is clear that jackshafts 19 and 2t; rotatemuch faster than hearth 11 due to the great gear reduction from theiackshafts to the hearth.

For example, in a preferred embodiment, we employ a 7 /2 horsepower 1200r.p.m. 230 volt electric motor. The differential 18 has about a 4 to 1reduction so that with the motor at full speed the jackshafts arerotating at approximately 300 revolutions per minute. This issubsequently very greatly reduced through the chain drives, reducinggear box and pinion gear to the hearth by approximately 5080 .10 1. Thusthe hearth makes abo t .06 revolution per minute or takes approximately17 minutes to make one revolution when rotating at full speed withoutinterruption. Given the distance of any point on the hearth from thehearth center, it is possible to compute the rate of hearth travel atthat point per revolution of jackshaft 20. For example, if the diameterof ring gear 27 is 55 feet, as it is in the described apparatus, we cancalculate by simple mathematics that hearth travel at the ring gear isapproximately .4 inch per revolution of jackshaft 20. This does not meanto suggest that motor 17 will be at full speed at all times and in factit will not; for in some instances motor 17 must be slowed down to allowarticles that require longer heating periods to be properly heated.However, regardless of the speed of motor 17, in the above example,hearth 11 will travel approximately .4 inch at ring gear 27 perrevolution of jackshafts 19 or 20 due to the unchanged gear reductionratio. The importance of such calculations will become apparent as thedescription continues.

Referring to FIGURE 2, we illustrate a disc 2% coaxiaily mounted onjackshaft v20 having holes 29 evenly spaced radially equidistantly inthe outer portion thereof. Disc 28 has a hub portion 3%} through whichjackshaft 29 passes. Hub 30 is secured to jackshaft 2% by set screw 31and 3 thus isc 28 rotates with jackshait it A photo-pickup .nbly 31. ismounted beneath jacksiiaft 23 on support Assembly comprises a dividedhousing 34 having t source such as an electric light bulb in portion 34an opposing photosensitive element in the other portion 345. Thephotosensitive element 34b is shielded by housing portion 34 from anylight source other than the light from 34a. Housing 34 is divided by agap 37 into which a portion of disc 28 intrudes. Disc 23 is positionedin gap 37 so as to interfere between the light from 34a. and tiephotosensitive element in 34b so that as disc 23 rotates with jackshaft2%, disc holes 29 will permit a beam of light from 34m to impinge uponthe photosensitive element in 3% as each of said holes 29 passesthercbetween. The number of holes 29 in disc 26 may be greatly variedaccording to the degree of control desired. The degree of control beingdirectly proportional to the number of holes 29. We have found that as apractical matter, twenty holes 29 in disc 28 provide a more thanadequate degree of control. Referring back to our earlier calculations,if the point on hearth 1?. at ring gear 27 travels .4 inch perrevolution of jackshaft 2%, then said point travels .02 inch per hole 2%on disc 28. Thus we provide -a control over the positioning of articleson hearth 11 to within .02 of an inch of hearth travel, which thoseskilled in the art will recognize is more than adequate for a rotaryhearth furnace.

Obviously, it is immaterial whether disc 28 and photopickup assembly 32are associated with jackshaft 19 or as described with jackshaft 29. Infact the positioning of said disc and pickup assembly may be on thedrive shaft of motor 17 or a shaft extending from the reducer gear box,gust as long as the shaft rotating disc 28 has a speed geared to andmuch higher than the hearth. We placed the disc and photo-pickupassembly on jackshaft 20 for several reasons including the conveniencefor servicing and available space.

Referring to FEGURES 2 and 3, it is clear that each time a hole 2.9permits a beam of light to pass from 34:! to the photosensitive elementin 34b an electric pulse is created in the photosensitive element. Theconstruction of the photosensitive element and its ability to create thedesec-ribed pulse is old and well known; likewise, light sourcessuitable for projecting beams in such circumstances are old and wellknown and thus these elements are not shown or further described herein.

Referring now to FIGURE 3, we diagrammatically show a pair of electroniccounters 38 and 39 connected to photo-pickup assembly 32, each of whichcounts the electrics1 pulses created in the photosensitive element.

from our earlier calculations, it is clear that each count made bycounter 38, and likewise counter 39, represents .02 inch of hearthtravel at ring gear 27. Counters 3% and 39 are selectively presettableto produce an electrical signal at any given number of pulses countecfrom 1 to 10,000 and can be coordinated to a secondary circuit tooperate relays or any other type of control when the desired count isreached. Such counters are available on the market (for example, see thecatalogue dated January 1, 1961 published by the Post ElectronicProducts Division of Reid Brothers Company, Inc. of Beverly,Massachusetts), and therefore will not be further described in detail.As shown in FIGURE 3, counters 38 and 39 are electrically connected to acontrol panel 40. Control panel as contains relay switches which respondto the electrical signals transmitted by the counters. These relayswitches, of course, control and operate the starters, drives andsubsequent controls shown in FIGURE 3. Control panel 46 is made up ofstandard hardware and circuitry well within the knowledge and skill ofthose skilled in the art and thus will not be further described indetail. In our invention, control panel 4% responds to signalstransmitted to it by counters 33 and 3% instead of signals transmittedto it by the hearth station switches earlier referred to. Likewise, thestarters, drives and subsequent controls controlled by panel J, asdiagrammatically shown more fully inFIGURE 3, are familiar to thoseskilled in the art and thus will not be described in detail. Sutlice itto say, that control panel 49 is preset to energize and deenergize theappropriate circuits which it controls as it receives the signals fromthe counters.

Very often, the operator will heating different sized articles such asbillets 14 and 15 which require different spacing on hearth 11. Thismeans that the charging and discharging rates will be different and thusthe station stops required for charging will be dilierent from thestation stops required for discharging. Therefore, hearth ll must bedivided up into one set of station stops for charging and another set ofstation stops for discharging. For this reason two counters arenecessary and in the present described embodiment counter 33 counts thelight pulses for charging stops and counter 39 counts the light pulsesfor discharging stops. Each counter is independently set to signal panel4% when it has counted a certain number of pulses. For example, ifbillets 14- each require 4.6 inches of hearth space adjacent ring gear27, then at the rate of .02 inch of hearth travel per pulse ascalculated earlier a billet 14 should be charged every 230 light pulses.This being the case, counter 33 is preset to signal panel 49 at every230 counts, at which signal panel 40 dcenergizes hearth travel motor 17and energizes the charging circuits to charge the hearth. Thus,jackshafts 19 and 20 are stopped and no further pulses are created untilthe charging is completed and the hearth drive circuit is reenergized bypanel To continue, if billets 15, which are being discharged, werepreviously placed on hearth 11 every 26 inches of hearth space at ringgear 27, then we can calculate that they must be removed every 1000light interruptions or pulses. This being the case, counter 39 is presetto signal panel n at every 1000 counts, at which signal panel 49 stopshearth Ill as just described above, and energizes the dischargingcircuits to discharge a billet 15 from hearth 11. Upon completion ofsaid discharge, panel 4%) again energizes the hearth drive circuit andthe hearth resumes its travel. In the above example, it is clear thathearth 11 will be stopped several times for charging before it will bestopped again for discharging and that the charging and dischargingstops are made independently of each other. Of course, once all ofbillets 3.5 are discharged and billets 14 are now ready for discharge,counter 38 will have to be reset to signal panel 40 at 230 counts todischarge billets 14. Thus, it is clear that hearth space can beutilized for the most efiicient spacing of articles to within .02 inchper article.

Even finer hearth divisions could be accomplished by increasing thenumber of holes 29 in disc 28 to lower the amount of hearth travel perlight pulse. However, as earlier stated, it is highly unlikely that afiner division than that provided by the twenty hole disc 28 would everbe desired. The counters can be set to signal at any pulse count from 1to as high as the operator would ever need to go. The exceptionalflexibility of our system is obvious and the earlier described occasionsfor changing cams or gears or for using less than the most eiiicientspacing of articles on the hearth, obviated.

In some instances, the hearth is capable of out-producing thecapabilities of the mill to which the articles being heated are to betransferred. To prevent a pile up of heated articles at the mill duringwhich time they may cool too much, we further provide a cycle time clock41 at the discharge end of the furnace. Clock 41 may be set todeenergize the hearth drive motor 17 for certain lengths of time. Forexample, if the mill can only take a billet 15 every seven minutes andthe hearth is producing one every five minutes it is necessary to delaythe hearth two minutes after each billet 15 is discharged. Thus, cycletime clock 41 is set to deenergize the hearth drive motor 1'7 for twominutes after the completion of each discharge operation. Of course,after clock 41 times out the hearth drive motor circuit is energized bycontrol panel at and hearth 1 1 will resume its travel. Cycle time clock41 may also be utilized to lengthen the heating cycle of articles thattake a longer period of time to become heated by the delaying actionjust described.

While we have shown and described a present pr ferred embodiment of theinvention, it is: to be distinctly understood that the invention is notlimited thereto but may he otherwise variously embodied within the scopeof the following claims.

We claim:

1. A rotary hearth furnace control comprising, in combination, a rotaryhearth furnace having a rotatable hearth, charging means deliveringarticles to be heated onto said hearth, discharging means removingheated articles from said hearth, hearth travel measuring means havingelectric pulse generating and pulse counting means and control meansoperatively responsive to said counting means coordinating the startingand stopping of the hearth and the energizing and deenergizing of thecharging means and discharging means.

2. A rotary hearth furnace control comprising, in combination, a rotaryhearth (furnace having a rotatable hearth, charging means deliveringarticles to be heated onto said hearth, discharging means removingheated articles from said hearth, hearth travel measuring means havingelectric pulse generating and pulse counting means and control meansoperatively responsive to said counting means where-by the hearth isstopped at predetermined stops for both charging and discharging saidhearth each independently of the other and then restarted.

3. A rotary hearth furnace control comprising, in combination, a rotaryhearth furnace having a rotatable hearth, charging means deliveringarticles to be heated onto said hearth, discharging means removingheated articles from said hearth, drive means having a drive shaftrotating said hearth, disc means coaxially mounted on said drive shafitand rotating therewith, a light source and photosensitive elementoperatively associated with said disc means whereby portions of saiddisc means permit the passage of light from said source to said elementas said disc means rotates, electronic counting means operable to countsaid light passages and control means operatively responsive to saidcount of light passages to stop and start the hearth and energize anddeenergize said charging means and discharging means.

4. A rotary hearth furnace control comprising, in combination, a rotaryhearth furnace having a rotatable hearth, charging means deliveringarticles to be heated onto said hearth, discharging means removingheated articles. from said hearth, drive means having a drive shaftrota-ting said hearth, disc means coaxially mounted on said drive shaftand rotating therewith, said disc means having alternately lighttransmitting and opaque portions, a light source and photosensitiveelement operatively associated with said disc means whereby saidtransmitting portions permit the passage of light from said source tosaid element as said disc means rotates, electronic counting meansoperable to count said light passages and control means operativelyresponsive to said count of light passages coordinating the stopping andstarting of the hearth and the energizing and deenergizing of thecharging means and discharging means including cycling means controllingthe duration of hearth stoppage.

5. A rotary hearth furnace control comprising, in combination, a rotaryhearth furnace having a rotatable hearth, charging means deliveringarticles to be heated onto said hearth, discharging means removingheated articles from said hearth, drive means having a drive shaftrotating said hearth, disc means coaxially mounted on said drive shaftand rotating therewith, said disc means having alternately lighttransmit-ting and opaque portions, a light source and photosensitiveelement operatively associated with said disc means whereby saidtransmitting portions permit the passage of light from said light sourceto said photosensitive element as said disc means rotates, electroniccounting means operable to count said light passages and control meansoperatively responsive to said count of light passages whereby thehearth is stopped at predetermined stops for both charging anddischarging said hearth each independently of the other and thereafterrestarted including cycling means controlling the duration of hearthstoppage.

6. A rotary hearth furnace control comprising, in combination, a rotaryhearth funa'ce having a furnace chamber with a rotatable hearth therein,charging means delivering articles to be heated into said chamber anddepositing them on said hearth, discharging means removing the heatedarticles from said hearth and chamber, hearth drive means including adrive shaft, disc means coaxially mounted on said shaft and rotatingtherewith, said disc means having alternately light transmitting andopaque portions, a light source and photosensitive element operativelyassociated with said disc means Whereby said transmitting portionspermit the passage of light from said light source to saidphotosensitive element as said disc means rotates, electronic countingmeans operable to count said light passages and control means responsiveto said count of light passages operable to stop said hearth drive meansand appropriately energize and deenergize said charging means anddischarging means including means operable to restart said hearthrotation and cycling means controlling the duration of stoppage of saidhearth.

7. A rotary hearth furnace control comprising, in combination, a rotaryhearth furnace having a furnace chamher with a rotatable hearth therein,charging means delivering articles to be heated into said chamber anddepositing them on said hearth, discharging means removing the heatedarticles from said hearth and chamber, hearth drive means including adrive shaft, disc means coaxially mounted on said shaft and rotatingtherewith, said disc means having alternately light transmitting andopaque portions, a light source and photosensitive element operativelyassociated with said disc means where by said transmitting portionspermit the passage of light from said light source to saidphotosensitive element as said disc means rotates, electronic countingmeans operable to count said light passages and control meansoperatively responsive to said count of light passages coordinatingstarting and stopping the hearth and appropriately energizing anddeenergizing the charging means and discharging means including cyclingmeans controlling the duration of hearth stoppage whereby the travel ofsaid hearth is interrupted at predetermined instances for both chargingand discharging said hearth each independently of the other.

References Cited in the file of this patent UNITED STATES PATENTS2,091,562 Palmer Aug. 31, 1937 2,622,861 Talley Dec. 23, 1952 2,656,106Stabler Oct. 20, 1953 2,865,103 Lolley et al. Oct. 23, 1958

1. A ROTARY HEARTH FURNACE CONTROL COMPRISING, IN COMBINATION, A ROTARYHEARTH FURNACE HAVING A ROTATABLE HEARTH, CHARGING MEANS DELIVERINGARTICLES TO BE HEATED ONTO SAID HEARTH, DISCHARGING MEANS REMOVINGHEATED ARTICLES FROM SAID HEARTH, HEARTH TRAVEL MEASURING MEANS HAVINGELECTRIC PULSE GENERATING AND PULSE COUNTING